buffer tube drilling question

hi all i have finished all of my 80% lower with the exception of the buffer tube hole,
so my question is
can i use a brake hone to open this hole up before i tap the threads
as i already have a starter hole, would this work as i am a bit scared of using that bigass drill bit i bought

About the slickest way I've seen that drilled a few years back was to put an empty upper on it and drill the buffer hole through the upper. That way the hole was centered with the upper. Can't remember the particulars on it and like most things the devil is in the details. Perhaps someone remembers where that was posted.

Hello earnie,
Drill bits often will not track right down the center where we want them to go. That's why they invented drill bushings and drill jigs... to guide the drill bit to where it is desired.

Another method is to use a milling machine to mill that hole properly centered then ream it to the minor diameter for the tap. A large verticle mill like a Bridgeport or a small horizontal mill will have a sufficient work envelope for this operation. It is most important to secure the work (AR receiver) and indicate-in the centerline before proceeding.

About 200 lbs clamping force is typical of most milling operations. Hollow areas should be supported/filled in with a block(s) of metal lest they get squashed.

To do the hand tapping I made a hand tapper machine as a student. The tapper uses a crank and a 2-jaw tap chuck rather like a little drill press. Mine also can be set to tap horizontally. The tapper table has T-slots to position the small vise as needed.

Earnie, no. No. Let me say it one last time. No. You will wind up with an off center or egg shaped hole. What resources do you have? Drill press? 90degree block? Drills? Reamer? Where are you located. If your nearby I could loan you the.proper tools. You could drill to one inch then adjustable ream to 1.124". Adj reamer are about $15. Or you could use a boring bar.

Hello earnie,
VZ58 has got that right. A brake hone removes a thou or two to create a sealing surface for a piston. They are not major metal movers !!!

One other method to look into is using a piloted boring bar or piloted drill bit in a drill press. This method assumes that the pilot hole there is in the proper location. Since the needed hole ends in a slant cut... an added pilot support bushing would be needed (like a bearing insert in the upper receiver locked together). This is a knock-off of moleman's suggestion. It can allow drilling or boring from the back end of the frame.

Use lots of black oil and go slow.its real easy to get off center and off axis. What size drill bit is it? Before I went cnc I would center spot, then 1/2", then 1", then boring bar or adj ream to 1.124" also some plans put the center of the hole .625", .629" and .632" above deck height. Most used milspec uppers seem to like .629" but I cut my upper and lowers with zero gap. My low pros like .632" if you have a gap when pivots are in then .625 or less may be your ticket.

i am modding my drill press to handle this task
the buffer tube hole was already started on this thing when i got it here are a few pics of what i have to work with, and of course building up the courage to hit this sucker